<template>
  <scroll
    class="listview"
    ref="listview"
    :data="data"
    :listenScroll="listenScroll"
    @scroll="scroll"
    :probeType="probeType"
  >
    <ul>
      <li class="list-group" v-for="(group, index) in data" :key="index" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li
            @click="selectItem(item)"
            v-for="(item, index) in group.items"
            :key="index"
            class="list-group-item"
          >
            <img v-lazy="item.avatar" :alt="item.name" class="avatar" />
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <!-- 侧边栏 -->
    <div
      class="list-shortcut"
      @touchstart="onShortcutTouchStar"
      @touchmove.stop.prevent="onShortcutTouchMove"
    >
      <ul class="needsclick">
        <li
          class="item"
          v-for="(item, index) in shortcutList"
          :key="index"
          :data-index="index"
          :class="{'current':currentIndex===index}"
        >{{item}}</li>
      </ul>
    </div>
    <!-- 滚动固定 -->
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>

    <!-- 加载动画 -->
    <div v-show="!data.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>
<script>
import Scroll from "base/scroll/scroll";
import { getData } from "common/js/dom";
import Loading from "base/loading/loading";
// 右边每个锚点的高度为18像素
const ANCHOR_HEIGHT = 18;
const TITLE_HEIGHT = 30;
export default {
  created() {
    this.touch = {};
    this.listenScroll = true;
    this.listHeight = [];
    this.probeType = 3;
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    };
  },
  // 给儿子传一些数据
  props: {
    data: {
      type: Array,
      default: []
    }
  },
  // 添加计算属性，在这里获取到右边固定title
  computed: {
    shortcutList() {
      return this.data.map(group => {
        return group.title.substr(0, 1);
      });
    },
    fixedTitle() {
      if (this.scrollY > 0) {
        return;
      }
      return this.data[this.currentIndex]
        ? this.data[this.currentIndex].title
        : "";
    }
  },
  methods: {
    refresh() {
      this.$refs.listview.refresh();
    },
    // 它是个子组件，只负责向外派发事件。它爸爸接受后决定是否激活，也就是singger.vue
    selectItem(item) {
      this.$emit("select", item);
    },
    onShortcutTouchStar(e) {
      // 获取索引值
      let anchorIndex = getData(e.target, "index");
      // 同时也记录一下一开始是第几个索引
      this.touch.anchorIndex = anchorIndex;
      // 记录touch的初始y值
      let firstTouch = e.touches[0];
      this.touch.y1 = firstTouch.pageY;
      this._scrollTo(anchorIndex);
    },
    onShortcutTouchMove(e) {
      // 右侧滑动时，左侧也要跟着滑动，我们需要在touchstart时候记录y的值
      // 两个函数共享的话，我们放到create里，为什么不放到data里，vue会自动帮我们监测，我们不需要监测
      let firstTouch = e.touches[0];
      this.touch.y2 = firstTouch.pageY;
      // 或0就是向下取整一样的，这里算出了偏移了几个锚点
      let delta = ((this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT) | 0;
      // 相应的我们就知道右边能移动几个group,再调用scrollToElement
      // 字符串和数字相加就会变成一个新的字符串，需要转化
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta;
      this._scrollTo(anchorIndex);
    },
    // 子组件给父组件发送的事件
    scroll(pos) {
      this.scrollY = pos.y;
    },
    // 相同的代码封装一下
    _scrollTo(index) {
      // 右侧快速滑动时点击最上面和最下面点击应该无效，可以这样设置
      if (!index && index !== 0) {
        return;
      }
      // 当它滑动时也要做相应的处理
      if (index < 0) {
        index = 0;
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2;
      }
      this.scrollY = -this.listHeight[index];
      // 第二个参数表示 我们不需要什么过渡动画
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0);
    },
    // 计算每个Group 的高度
    _calculateHeight() {
      this.listHeight = [];
      const list = this.$refs.listGroup;
      let height = 0;
      this.listHeight.push(height);
      for (let i = 0; i < list.length; i++) {
        // 获取到每一个Group
        let item = list[i];
        // 因为是dom元素，可以直接是clientHeight
        height += item.clientHeight;
        this.listHeight.push(height);
      }
    }
  },
  // 监测数据变化，有变化后重新渲染
  watch: {
    data() {
      // 把data挂载到DOM上是有时间的
      setTimeout(() => {
        // data一旦变化立马重新更新数据
        this._calculateHeight();
      }, 20);
    },
    // 监听scrollY的变化
    scrollY(newY) {
      const listHeight = this.listHeight;
      // 当滚动到顶部
      if (newY > 0) {
        this.currentIndex = 0;
        return;
      }
      // 当滚动到中间
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i];
        let height2 = listHeight[i + 1];
        // 当它在height1和height2之内，获取索引值
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i;
          // 计算diff的值，就是上限和下限之间的距离
          this.diff = height2 + newY;
          return;
        }
      }
      // 当滚动到底部，-newY大于最后一个元素的上限
      this.currentIndex = listHeight.length - 2;
    },
    diff(newVal) {
      let fixedTop =
        newVal > 0 && newVal < TITLE_HEIGHT ? newVal - TITLE_HEIGHT : 0;
      if (this.fixedTop === fixedTop) {
        return;
      }
      this.fixedTop = fixedTop;
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`;
    }
  },
  components: {
    Scroll,
    Loading
  }
};
</script>
<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~common/stylus/variable';

.listview {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: $color-background;

  .list-group {
    padding-bottom: 30px;

    .list-group-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }

    .list-group-item {
      display: flex;
      align-items: center;
      padding: 20px 0 0 30px;

      .avatar {
        width: 50px;
        height: 50px;
        border-radius: 50%;
      }

      .name {
        margin-left: 20px;
        color: $color-text-l;
        font-size: $font-size-medium;
      }
    }
  }

  .list-shortcut {
    position: absolute;
    z-index: 30;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 20px;
    padding: 20px 0;
    border-radius: 10px;
    text-align: center;
    background: $color-background-d;
    font-family: Helvetica;

    .item {
      padding: 3px;
      line-height: 1;
      color: $color-text-l;
      font-size: $font-size-small;

      &.current {
        color: $color-theme;
      }
    }
  }

  .list-fixed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;

    .fixed-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }
  }

  .loading-container {
    position: absolute;
    width: 100%;
    top: 50%;
    transform: translateY(-50%);
  }
}
</style>
